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MAINTENANCE README FOR PCRE
---------------------------
The files in the "maint" directory of the PCRE source contain data, scripts,
and programs that are used for the maintenance of PCRE, but which do not form
part of the PCRE distribution tarballs. This document describes these files and
also contains some notes for maintainers. Its contents are:
Files in the maint directory
Updating to a new Unicode release
Preparing for a PCRE release
Making a PCRE release
Long-term ideas (wish list)
Files in the maint directory
----------------------------
Builducptable A Perl script that creates the contents of the ucptable.h file
from two Unicode data files, which themselves are downloaded
from the Unicode web site. Run this script in the "maint"
directory.
ManyConfigTests A shell script that runs "configure, make, test" a number of
times with different configuration settings.
Unicode.tables The files in this directory, Scripts.txt and UnicodeData.txt,
were downloaded from the Unicode web site. They contain
information about Unicode characters and scripts.
ucptest.c A short C program for testing the Unicode property functions
in pcre_ucp_searchfuncs.c, mainly useful after rebuilding the
Unicode property table. Compile and run this in the "maint"
directory.
ucptestdata A directory containing two files, testinput1 and testoutput1,
to use in conjunction with the ucptest program.
utf8.c A short, freestanding C program for converting a Unicode code
point into a sequence of bytes in the UTF-8 encoding, and vice
versa. If its argument is a hex number such as 0x1234, it
outputs a list of the equivalent UTF-8 bytes. If its argument
is sequence of concatenated UTF-8 bytes (e.g. e188b4) it
treats them as a UTF-8 character and outputs the equivalent
code point in hex.
Updating to a new Unicode release
---------------------------------
When there is a new release of Unicode, the files in Unicode.tables must be
refreshed from the web site, and the Buildupctable script can then be run to
generate a new version of ucptable.h. The ucptest program can be used to check
that the resulting table works properly, using the data files in ucptestdata to
check a number of test characters.
Preparing for a PCRE release
----------------------------
This section contains a checklist of things that I consult before building a
distribution for a new release.
. Ensure that the version number and version date are correct in configure.ac,
ChangeLog, and NEWS.
. Run ./autogen.sh to ensure everything is up-to-date.
. Compile and test with many different config options, and combinations of
options. The maint/ManyConfigTests script now encapsulates this testing.
. Run perltest.pl on the test data for tests 1 and 4. The output should match
the PCRE test output, apart from the version identification at the top. The
other tests are not Perl-compatible (they use various special PCRE options).
. Test with valgrind by running "RunTest valgrind". There is also "RunGrepTest
valgrind", though that takes quite a long time.
. It may also useful to test with Electric Fence, though the fact that it
grumbles for missing free() calls can be a nuisance. (A missing free() in
pcretest is hardly a big problem.) To build with EF, use:
LIBS='/usr/lib/libefence.a -lpthread' with ./configure.
Then all normal runs use it to check for buffer overflow. Also run everything
with:
EF_PROTECT_BELOW=1 <whatever>
because there have been problems with lookbehinds that looked too far.
. Test with the emulated memmove() function by undefining HAVE_MEMMOVE and
HAVE_BCOPY in config.h. You may see a number of "pcre_memmove defined but not
used" warnings for the modules in which there is no call to memmove(). These
can be ignored.
. Documentation: check AUTHORS, COPYING, ChangeLog (check date), INSTALL,
LICENCE, NEWS (check date), NON-UNIX-USE, and README. Many of these won't
need changing, but over the long term things do change.
. Man pages: Check all man pages for \ not followed by e or f or " because
that indicates a markup error.
. When the release is built, test it on a number of different operating
systems if possible, and using different compilers as well. For example,
on Solaris it is helpful to test using Sun's cc compiler as a change from
gcc. Adding -xarch=v9 to the cc options does a 64-bit test, but it also
needs -S 64 for pcretest to increase the stack size for test 2.
Making a PCRE release
---------------------
Run PrepareRelease and commit the files that it changes (by removing trailing
spaces). Then run "make distcheck" to create the tarballs and the zipball.
Double-check with "svn status", then create an SVN tagged copy:
svn copy svn://vcs.exim.org/pcre/code/trunk \
svn://vcs.exim.org/pcre/code/tags/pcre-7.x
Don't forget to update Freshmeat when the new release is out, and to tell
webmaster@pcre.org and the mailing list.
Future ideas (wish list)
------------------------
This section records a list of ideas so that they do not get forgotten. They
vary enormously in their usefulness and potential for implementation. Some are
very sensible; some are rather wacky. Some have been on this list for years;
others are relatively new.
. Optimization
There are always ideas for new optimizations so as to speed up pattern
matching. Most of them try to save work by recognizing a non-match without
having to scan all the possibilities. These are some that I've recorded:
* /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
OTOH, this is pathological - the user could easily fix it.
* Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
to have little effect, and maybe makes things worse.
* "Ends with literal string" - note that a single character doesn't gain much
over the existing "required byte" (reqbyte) feature that just saves one
byte.
* These probably need to go in study():
o Remember an initial string rather than just 1 char?
o A required byte from alternatives - not just the last char, but an
earlier one if common to all alternatives.
o Minimum length of subject needed.
o Friedl contains other ideas.
. If Perl gets to a consistent state over the settings of capturing sub-
patterns inside repeats, see if we can match it. One example of the
difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
because I think it needs much more state to be remembered.
. Perl 6 will be a revolution. Is it a revolution too far for PCRE?
. Unicode
* Note that in Perl, \s matches \pZ and similarly for \d, \w and the POSIX
character classes. For the moment, I've chosen not to support this for
backward compatibility, for speed, and because it would be messy to
implement.
* A different approach to Unicode might be to use a typedef to do everything
in unsigned shorts instead of unsigned chars. Actually, we'd have to have a
new typedef to distinguish data from bits of compiled pattern that are in
bytes, I think. There would need to be conversion functions in and out. I
don't think this is particularly trivial - and anyway, Unicode now has
characters that need more than 16 bits, so is this at all sensible?
* There has been a request for direct support of 16-bit characters and
UTF-16. However, since Unicode is moving beyond purely 16-bit characters,
is this worth it at all? One possible way of handling 16-bit characters
would be to "load" them in the same way that UTF-8 characters are loaded.
. Allow errorptr and erroroffset to be NULL. I don't like this idea.
. Line endings:
* Option to use NUL as a line terminator in subject strings. This could now
be done relatively easily since the extension to support LF, CR, and CRLF.
If this is done, a suitable option for pcregrep is also required.
. Option to provide the pattern with a length instead of with a NUL terminator.
This probably affects quite a few places in the code.
. Catch SIGSEGV for stack overflows?
. A feature to suspend a match via a callout was once requested.
. Option to convert results into character offsets and character lengths.
. Option for pcregrep to scan only the start of a file. I am not keen - this is
the job of "head".
. A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
preceded by a blank line, instead of adding it to every matched line, and (b)
support --outputfile=name.
. Consider making UTF-8 and UCP the default for PCRE n.0 for some n > 7.
. Add a user pointer to pcre_malloc/free functions -- some option would be
needed to retain backward compatibility.
. Define a union for the results from pcre_fullinfo().
. Provide a "random access to the subject" facility so that the way in which it
is stored is independent of PCRE. For efficiency, it probably isn't possible
to switch this dynamically. It would have to be specified when PCRE was
compiled. PCRE would then call a function every time it wanted a character.
. Wild thought: the ability to compile from PCRE's internal byte code to a real
FSM and a very fast (third) matcher to process the result. There would be
even more restrictions than for pcre_dfa_exec(), however. This is not easy.
. Should pcretest have some private locale data, to avoid relying on the
available locales for the test data, since different OS have different ideas?
This won't be as thorough a test, but perhaps that doesn't really matter.
. pcregrep: add -rs for a sorted recurse? Having to store file names and sort
them will of course slow it down.
. Someone suggested --disable-callout to save code space when callouts are
never wanted. This seems rather marginal.
. Check names that consist entirely of digits: PCRE allows, but do Perl and
Python, etc?
Philip Hazel
Email local part: ph10
Email domain: cam.ac.uk
Last updated: 09 August 2007
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